The present invention relates to a diving mask and more particularly to a diving mask having a drainage mechanism provided with a check valve.
Diving masks are well known which have a drainage mechanism provided with a check valve. For example, U.S. Pat. No. 5,890,234 (Reference 1) and U.S. Pat. No. 5,979,441 (Reference 2) disclose a diving mask comprising a nose cover formed integrally with a skirt member and an annular member attached to a bottom of the nose cover. The annular member includes a plurality of drain holes and a check valve adapted to be opened outward with respect to these drain holes. The check valve is normally held in close contact with a valve seat formed on the annular member. The annular member is previously formed using material different from material for the skirt member and set in a die when the skirt member is molded in this die so that the annular member may be integrated with the skirt member.
Conventionally, the annular member including the valve seat is formed using a plastic or metallic material is a relatively hard and deformation-resistant while the skirt member is formed using a soft and elastic rubber-like material. The annular member is provided with an annular projection having a height in a range of about 0.3 to about 0.5 mm serving as the valve seat. Generally, such annular member is set in the die used to mold the skirt member at a predetermined position of the die. Molten plastic material is injected at a high pressure into the closed die to obtain the skirt member including the nose cover integrated with the annular member. However, such a process of molding the skirt member may be often accompanied with a problem such that the molten plastic material flows to the annular member and partially covers the valve seat. Obviously, the valve seat should not be covered with the plastic material. The amount of the plastic material partially covering the valve seat in this manner refers to as flash and it is impossible to ensure that the check valve is normally held in close contact with the valve seat so far as such flash is not removed.